Synthesis and structural characterization of azine based oligoesteric chemosensors for Fe2+ ion detection

Abstract

AbstractAzine‐based monomer and its three oligoesters were synthesized, characterized with IR, UV, GC‐MS, GPC, 1H NMR, 13C{1H} NMR, 31P NMR and applied to chemosensor applications. In the chemosensor study, fluorophores show selective and sensitive responses with Fe2+ ions in the DMF/H2O solution (1 : 1, pH: 7.4, fluorophore: 5 μM). The quenching of fluorescence intensity with the addition of Fe2+ ion gives the correlation coefficient (R2) value above 0.99286, exhibiting good binding stoichiometry nature of fluorophores with Fe2+ than the oligoesters. The high detecting capability of oligoesters is further ascertained by its higher LOD than the monomer (5.05×10−7). The binding constant values of fluorophores obtained from the Benesi‐Hildebrand plot show that the oligoesters have a higher binding ability (1.0012–1.0025 M−1) with Fe2+ ion than the monomer (1.0011 M−1). The conductivity nature of the oligoester gradually increased with the contact time of iodine. After 96hr of iodine doping, EMDAP exhibits higher conductivity (1.98×10−3 Scm−1) than the other oligoesters due to higher electron‐density nitrogen atoms in the structure. The EMDOP shows high dielectric constant value because of its π‐π interaction, loosely attached π electrons and high dipole moment values. All these experimental results are validated with the theoretical (DFT) approach by optimizing the structure of the fluorophore with B3LYP/6‐311++G(d,p) level basis set. The DFT approach also explains the mechanism of fluorescence quenching and the exact binding sites of fluorophores with Fe2+ ions.